1. Technical Field
The present invention relates to a droplet discharge head and a droplet discharge device.
2. Related Art
Multi-layered substrates made of low temperature co-fired ceramics (LTCC) are widely used for a substrate of a high frequency module, a substrate of an IC package, and the like due to their excellent high-frequency property and high heat-resistance. In a method for manufacturing an LTCC multi-layered substrate, a step in which a circuit pattern is drawn on a green sheet with a metal ink and a step in which a plurality of green sheets are layered so as to be fired all together are commonly conducted.
In terms of the step in which a circuit pattern is drawn, JP-A-2005-57139, as a first example, discloses an ink-jet method in which a metal ink is discharged as fine droplets for densifying the circuit pattern. By the ink-jet method, one circuit pattern is drawn with a lot of droplets. A bulk of one droplet is several to several dozen picoliters. The ink-jet method enables the circuit pattern to be fine and have a narrow pitch by changing discharge positions of the droplets. However, if the circuit pattern made from droplets is dried in a dry furnace, a heating treatment is conducted on the whole of the green sheet, increasing a heat load imposed on the circuit pattern and the green sheet.
Therefore, for the ink-jet method, proposals for resolving the above problem have been conventionally made. In JP-A-2006-247529 as a second example, JP-A-2006-248189 as a third example, and JP-A-2006-247622 as a fourth example, a droplet discharge head that discharges droplets is provided with a laser emitting part and irradiates a droplet that is discharged with laser light so as to dry the droplet in a moment. Laser light emitted by the laser emitting part supplies an amount of heat required only for a region of the droplets. Therefore, thermal damage of the circuit pattern and the green sheet can be substantially avoided. As a method for manufacturing such laser emitting part, JP-A-2003-197881 as a fifth example proposes that a vertical cavity surface emitting laser (VCSEL) is formed on a lattice-matching substrate and then the vertical cavity surface emitting laser is separated from the substrate so as to be bonded to other base. Thus, a laser emitting part can be provided to a substrate lattice-mismatching with the laser emitting part. As a method for manufacturing an optical member required for the laser emitting part, JP-A-2004-119581 as a sixth example proposes that a micro-lens is formed on an emitting face of the laser emitting part by the ink-jet method. Accordingly, an emission angle and a wavelength of laser light emitted from the vertical cavity surface emitting laser can be controlled with higher accuracy.
In the ink-jet method, an object and a droplet discharge head are relatively moved so as to draw a circuit pattern having a desired shape. A droplet on the object passes a spot of laser light in such a momentary period of time that the object and the droplet discharge head relatively move, that is, in such a momentary period of time that the droplet and the laser emitting part relatively move. Thus, an irradiation time with the laser light is decreased due to the relative move.
A forming pitch of nozzles provided to the droplet discharge head is several dozen μm to several hundred μm. A spot size of the laser light has to be nearly same as the forming pitch of the nozzles so as to irradiate each droplet with the laser light. Thus, since the spot size of the laser light is small, a time for irradiating the droplets with the laser light is further decreased.
In order to dry the droplets, the region for the droplets has to be irradiated with the whole energy required for the drying in such short irradiation time described above. However, irradiation of laser light having high energy with respect to the droplets of several to several dozen picoliters causes bumping of the droplets instantly, eliminating the circuit pattern near the droplets. On the other hand, in a case of emitting laser light having low energy, a moving velocity of the droplet discharge head with respect to the substrate has to be sufficiently slow. Therefore, productivity of various patterns is substantially degraded.